Acoustic method for driving piles



July 6, v1965 A. G. BoDlNE ACOUSTIC METHOD FOR DRIVING PILESv f OriginalFiled Jan. 24. 1958 2 Sheets-Sheet 1 FI G. 3

ATTORNEY A. G. BODINE ACOUSTIC METHOD FOR DRIVING PILES Original FiledJan. 24. 1958 2 Sheets-Sheet-2 PILE DISPLACEMENT RESULTANT LOWER ENDDISPLACEMENT WAVE ROTDR ROTATION INVENTOR.

ALBERT G. BODINE ATTORNEY United States Patent O 3,193,027 ACUUSTRCl/ETHOD FCR DRIVING PELES Albert G. Bottine, Los Angeles, Calif'. (7877Woodley Ave., Van Nuys, Calif.)

Original application lan. 24, 1958, Ser. No. 710,956, new Patent No.3,054,463, dated Sept. 18, 1962. Divided and this application Mar. 29,1962, Ser. No. 183,698

6 Claims. (Ci. 175--19) This invention deals generally with methods fordriving piles, such as are used for building or other structuralfoundations, and is applicable to pile driving either into dry-surfaceearth, into marsh or tidewater ground, or in underwater situations. Thepiles in contemplation are those conventionally used, typically, steelH-section members, members of corrugated section, tubular section, orany other, and composed of steel, wood, prestressed concrete, plastic,etc.

The present application is a continuation-in-part of my priorapplication entitled, Acoustic Method and Apparatus for Driving Piles,Serial No. 644,774, filed March S, 1957, now Patent No. 2,975,846 and adivision of my co-pending application Serial No. 710,956, filed January24, 1958 for Apparatus for Driving Piles, now Patent No. 3,054,463.According to the disclosure in said patent application, a pile is drivenby use at its upper end of an elastic wave generator, which sets thepile into standing wave vibration, and causes it, when rested on theearth, to be driven downwardly therein. The pile initially vibrates as afree-free bar, with a velocity antinode at each end, and a node at themidpoint. The pile, undergoing such standing wave action, alternatelyelastically elongates and contracts; and the resulting impacts of thelower end of the pile on the earth drive it down. As disclosed in saidparent application, one or more additional velocity antinodes may appearalong the pile, depending upon harmonic wave frequencies generated inrelation to the length of the pile. Such additional antinodes maintainthe pile in active vibration along increased stretches of its totallength, and are thus useful in reducing static friction between theembedded length of the pile and the surrounding earth. Such reduction instatic friction, of course, greatly facilitates the penetration of thepile deep into the earth.

An object of the present invention is the provision of a pile drivingmethod of the general type mentioned, including the additional step ofpositively introducing harmonic wave components, and therefore one ormore additional velocity antinodes, into the wave pattern establishedalong the pile.

I have found that the present invention may be practiced by simplyconnecting in a second wave generator,

' of proper wave frequency, so as to provide the desired additionalvelocity antinodes. That is to say, one generator may be used togenerate the fundamental frequency standing wave providing a velocityantinode at each end of the pile; and an additional generator is used toprovide a harmonic standing wave, for instance, the second harmonic,creating a velocity antinode at the location of the midpoint nodetending to be produced by the first generator. I have also found that aWave generator may be used which produces both wave patternssimultaneously-the fundamental having a velocity an- ICC tinode at eachend, and the harmonic involving one or more additional velocityantinodes between the ends.

A number of benefits result from the invention. In the first place, asmentioned hereinabove, the additional antinode or antinodes means anextended distribution of vibration along the pile, and therefore reducedstatic friction in intermediate regions of the pile which are somewhatdead or inactive when using a fundamental frequency standing wavecharacterized by a node at the midregion. The additional antinode orantinodes are very effective in overcoming static friction as the pileprogresses into the earth,

In addition, by use of harmonic frequencies along with the fundamental,improved motion characteristics may be given the lower end of the pile,with increase in both the stroke amplitude and velocity with which thepile impacts against the earth.

A further object of the invention is the improvement of acoustic piledriving equipment, irrespective of harmonic frequency generation.

The invention will be more fully understood from the following detaileddescription of an illustrative embodiment thereof, reference for thispurpose being had to the accompanying drawings, in which:

FIGURE l is a schematic elevational view of a pile driving system inaccordance with the invention, equipment for lifting the system intoposition for operation being omitted from the drawings;

FiGURE 2 is a section taken on line 2-2 of FIG- URE 1;

FlGURE 3 is a section on line 3 3 of FIGURE 2; and

FIGURE 4 is a chart illustrative of wave action in the pile inaccordance with the invention.

ln FIGURES l and 2, numeral 10 designates generally a cylindrical pile,with its lower end in engagement with the earth 11, and with its upperend carrying a pile driving assembly 12 in accordance with theinvention, equipment for hoisting the apparatus into the position shown,and for suspending it in such position, being omitted from the drawing.It will be understood, however, that any suitable hoisting equipmentsuch as a crane and block and tackle equipment furnished with a hookengageable with the eye 13 at the upper end of the pile drivingassembly, may be used. Suitable equipment of this nature is shown in myaforesaid application Serial Number 644,774. It may also be mentioned atthis point that while l have shown in FlGURES 1 and 2 a simple form ofcylindrical pile, other forms such as H-section steel piles, or otherknown or suitable forms, are suitable to the practice of the invention,provided only that they have a degree of elasticity permitting necessarystanding Wave action therein.

The pile driving assembly 12 includes an adapter 14 comprising a socket15 adapted to receive the upper end portion of the pile lil. Extendingupwards from this adapter 14 is a reduced tubular stern 16, closed atits upper end, as indicated at 17, and formed at the top with a threadedsocket 18 into which is screwed a threaded coupling member 19, formed onthe lower end of the cylindrical hollow body or barrel 20 of vibrationgenerator 21. Generator 21 is driven from a pair of electric motors 22and 23 fixedly mounted in a cylindrical casing 24, which is tightlymounted at its lower end on top of a heavy cylindrical body 25, providedwith a cen- Ip el? tral longitudinal bore 25 which receives theaforementioned stem 16 with a small clearance as indicated.V A bearingbushing 27. fitted in body 25 at the upper end of bore 26 supports stem16 or free vertical sliding movement, and near the lower` end of thebody 25, a packing unit 28 is mounted for packing the stem 15.

A large bore 36 extending upwardly into the lower end of body 25 aifordsa cylinder` in which works a piston prises a device for generating andapplying to the upper end of stem 16, and thence,rthrough ,adapter 14 tothe upper end of pile 10, a vertically-directed alternating force havingboth fundamental and harmonic wave frequencies capable of resonating`the pile 1t).V That is'to say, the vibration generator :applies to thepile a complex force wave Whichsets up in the pile both a fundamentaland a A harmonicresonant standing wave, or in still other language, setsup in the pile a complex standing wave action which is the resultant ofVa fundamental half-wavelength l standing wave, and a harmonic thereof,in this case the -second harmonic. AThe generator includes theaforementioned tubular housing 20, screw coupled at its lower end to theupper endofthe aforementioned stem 16. The

upper end of housing 2t) is closed by means of va clos-ure or plugmember 40. ,The housing 2d encloses a seriesof,

vertically spa-ced, fundamental-frequency unbalanced rotors 41,"in thiscase Vfour yin number, and in addition,` a

in the same direction, while` the two intermediate rotors 41 .rotate inthe'same di-rection, but in the opposite direction to the upper andlower rotors. Accordingly, lateral components ofV force are balancedout. Likewise, couples tending to. rotate .the generator about'atransverse axis are avoided. According to the illustrative arrangement,two double frequency rotors 42 are used, but it is This bottom plate 32is pro- Y to be understood that, for a stronger second harmonic,

additional double frequencyrotors 42 may be added. Be-

cause of the half-size of the rotors 42 as compared with the rotors 41,necessitated by the half-size gears 45, the forces contributed by theindividual .rotors 42 will be slightly less than the for-ces contributedby the rotors 41, even though the smaller rotorsv operate attwice thecentrifugal speed. It will be obvious that t-he number of rotors 42 maybe increased as much as desired, so that any desired relationshipbetween forces generated by the rotors 41 and the rotors 42 may beachi-eved. It is evident that by a su-itable increaseinthe number ofrotors 42, the total force exerted thereby may, for example, be madeequal to the total force generated by the rotors 41.' The rotors 42 arephased to move vertically in synchronism with one another, so that thevertical components of force will be additive, whereas the horizontalcomponents of force will be cancelled. Double frequency rotors 42,moreover, may be various phase relationships to the fundamentalfrequency rotors 41 within the broad scope of the invention. However,preferably, particularly for driving in hard formation Vthe rotor-s 42are phased as illustrated in FEGURES 2 and 3, such that they are at themidpoint of their downstrokes while the upper rotors 41 are both at thetop and'at the Ybottom of their strokes. Thus, in FEGURES 2 and 3, thefundamental frequency rotors 41 vare all at the .top of their strokeswhile therotors 42 are series of harmonic frequency Vunbalanced rotorsv42, in 'Y this case two in number. These rotors are all rotatablymounted on transverse shafts 43 set tightly into the walls of housing20. The rotors 4-1'include intermeshing gears 44, and the rot-ors42finclude lintermes'hing gears 45. In-

the illustrative embodiment, the rotors 41 are separated into two upperrotors and two lower rotors, interconnected by an idler gear 47 on ashaft 48 rotatably mounted in suitable bearings in the walls of housing2t). The gearr of upper-most rotor 42 meshes with the gear of thelowermost rotor 41. Gears 45 of harmonic frequency rotors 42 are halfthe diameter of the gears 44 for fundramental frequency rotors 41, sothat rotors 42 turn at twice the angular velocity of rotors 41. In otherwords, rotors 42 make two revolutions for each revolution of rotors 41,and are therefore of double orfsecond harmonic frequency.

Gear 44 for uppermost rotor 41 is -driven by pinion 50 f on rotatableshaft 51, carrying a bevel gear pinion 52` rIhe motors 22 and 23 arevariable speed electric motors, and may be, for example, inductionmotors driven by power at variable'frequency frorn'a generator having asa prime mover a variable speed gas engine.

stances an ordinary yinduction load will have enough,

at `the midpoint of their downstrokes. It Will also be evident that whenthe rotors 41 are at the bottom of their downstrokes, the Irotors 42will again be at the midpoint of their ldownstrokes.` As mentioned,other phase relationshipsare possible, an example of which will bedescribed later, but that here shown and described is preferr-ed.l y

To Vdrive a pile,the pile with `the driving assembly 12 fit-ted to itsupper end, is Ihoisted into the position shown in FIGURE 1, and motors22 and23 are Iopera-ted through power furnished via conductors indicatedat 60 and 61. The motors drive .the generator shaft 56, rotating theunbalanced rotors 41 andj42.` This results in a complex valternatingforce being generated in a-verticaldirection, the force from eachunbalanced Arotor being exerted through its mounting shaft onto thegenerator housing 20, andy being thence applied to the upper end of Stem16, and yfrom the lower endof stemlo through adapter .14 -to the Y upperend of the pile 10. Air under pressure is main- In some inslip so thatit can be driven by a regular 60cycle or other suitable fixed frequencysource.

The unbalanced fundamental frequency `rotors 41 are so 'phased withrelation to one ano-ther that allof their unbalanced or eccentric weightportions move up and down in synchronism with one another. The verticalcom- -ponents of force owing to these unbalanced rotors are therefore inphase and additive. f

It will be seen that the upperand lower rotors 41 rotate tain-ed in thepiston chamber above the piston 31 during operation, and it will be seenthat the weight of the massive body 25, the easing 24, .and the drivemotor-s 22 and V215, isy supported on thepiston 31 through the body ofair undercompres'sion above the latter. This weightfis transferredfrompiston 31 tostem y16 and adapter 14 and thence to theupperend yofthe pile, whereby the pile is blased downwardly by a substantial weight.The body of air under compression betweenV the piston 31 and the heavylbody 25 th-us acts asan ainspring, permitting relative verticalvibration of vibration generator 21, stem 16, adapter 14 and the upperend portion of the pile relative to the massive body 25, casing 24 andthe motors 22 and 23. The splined driving connection at 56, 57 permitsrelative reciprocation V,at that point. Y

Motors 22 vand 23 are operated at a speed such as to cause thefundamental frequency rotors 41 to generate a vertically-directedalternating force at a frequency which 1s a resonant frequency of pile10 fora longitudinal mode of standing wavevibration of the pile.Usually, and preferably, the frequency lof the rotorsr41 is made such asto generate a half-wavelength standing wave in the pile,

so that the pile acts as a free-free bar, with velocity .antinodes atits ends, and a stress antinode at the midpoint. Under these conditions,and disregarding for the time beling the double frequency rotors 42, thetwo upper and lower half-lengths of the pile alternately elasticallyelongate and .contract in step with one another, the cumulativeamplitude of the elastic deformation or displacement, measured from thenodal midpoint of the pile, progressive'ly increasing toward each end.The midpoint of the pile, if it wehe not for the double frequencyrotor-s 42, would under the circumstances assumed have no substantialvibration.

For a complete understanding of the invention, reference is nextdirected to the chart of FIGURE 4, and first to part A thereof,illustrating the just-described standing wave action of the pile whensubjected only to the alternating force exerted by the synchronizedfundamental frequency rotors 41. The pile is designated again by thenumeral l0, and is shown in ve successive positions, corresponding tosuccessive 90 spaced positions of the rotors 41, so that one completecycle of vibration is represented. The midpoint of the pile, at A, B andD, is marked for identification with a short horizontal line m. Thecorresponding position of one of the synchronized rotors 41 is shownover the pile in each position of the pile. 1For simplicity we areassuming the typical case where pile motion is in phase with rotorforce. The solid arrows below the representations of the rotor representthe direction of the force exerted by the rotor on the pile in thatposition. The dotted arrows indicate the components of vertical velocityof the rotors. The alternating force exerted on the pile, at thefundamental frequency for half-wavelength standing wave vibration of thepile, causes the pile to alternately elastically contract and elongate,as represented in the successive pile positions shown. It will beobserved that the vertical force wave lags the vertical component ofrotor velocity by 90. Thus, for example, at the 90 position, the rotoris rising at maximum velocity, but the vertical force exerted thereby iszero. At 180, the rotor is at the top, exerting a maximum upward forcecomponent (by reason of its centrifugal force), while its verticalcomponent of velocity is zero. It will further be seen that thelongitudinal displacements of the pile lag the vertical force wave by90. Thus, in the first position, the rotor 41 is at the bottom, exertinga maximum downward force, the vertical velocity of the rotor is zero,and the pile is at its normal length, but is contracting at maximumvelocity. In the second position, 90 later, the rotor is rising atmaximum velocity, vertical force is zero, the pile is contracted to itsminimum length, and is momentarily at zero vertical velocity. Theconditions for the third, fourth and fifth positions will be readilyunderstood from the diagrams.

In FIGURE 4, at C, is shown in dashed lines a sinusoidal wave 70representing the displacement of the lower end of the pile above andbelow the zero (normal length) axis for the fundamental frequency actiondepicted at A. This curve will be seen to be the same as the dashed linecurve drawn through the lower end of the pile in the successivepositions shown at A. This wave 70 is one component of the resultantcomplex lower end displacement wave, as will appear presently.

At B in FIGURE 4 are shown successive positions of the pile with onlythe wave action therein owing to the double frequency or second harmonicrotors 42. In other words, the positions at B show only the secondharmonic action, the pile being assumed as having no fundamentalfrequency action. The actual overall action, of course, is the resultantof the two component actions represented at A and B. The second harmonicwave is characterized by a velocity antinode at each end of the pile andat the midpoint thereof, with stress antinodes at the quarter andthree-quarter points. Accordingly, the two half-lengths of the pileelongate and contract with 180 phase difference. In other words, onehalf-length elongates as the other contracts, and vice versa. The twocomponent wave actions shown at A and B are in the phase relationpreviously described, i.e., with the harmonic rotors 42 at the midpointsof their downstrokes while the fundamental frequency rotors are passingthrough both the upper and lower ends of their strokes. In the secondharmonic case, B, as in the fundamental, A, the vertical alternatingforce component exerted on the pile by the second harmonic rotors 42lags the vertical component of rotor velocity by Further, thelongitudinal displacements 0f the pile ends lag the vertical force waveby 90. In the fundamental frequency case A, however, the two ends of thepile move equally and oppositely, while in the second harmonic case B,the two ends of the pile move equally, but in the same direction.

sinusoidal dash-line wave 71 at C represents the displacement of thelower end of the pile owing to the second harmonic wave action depictedat B. Curve 72, at C, is the resultant of curves 70 and 71, andrepresents the complex motion of the lower end of the pile owing to thecombined fundamental and second harmonic wave actions represented at Aand B. It will be observed that the wave 72 representative of themotions of the lower end of the pile includes a peaked double amplitudeportion 73. The slope of the sides of this wave portion 73 representsthe velocity of downward motion of the pile, and it will be seen fromthe curve that the pile is quickly accelerated to a high velocity, andthen travels downward at this high velocity for a substantial distance,followed by a sharp deceleration at the bottom. This action isespecially effective in breaking and penetrating hard formation.

At D is represented an alternative phase relation of the second harmonicrotor 42 to the fundamental frequency rotor 41 of A. In this case, therotors 41 and 42 pass through the lower ends of their strokes together.The fundamental frequency lower pile-end displacement wave component isindicated at E by reference numeral 71a. The resultant complex motion ofthe lower pile-end is shown at 72a, and it will be observed thatsubstantial amplitude and downward velocity are again attained.

The combination of the fundamental and second harmonic waves thusprovides an effective wave form for the motion of the bottom end of thepile.

A very important benefit of the invention, however, is the creation ofan additional velocity antinode at the midpoint of the pile, whereby theentire length of the pile is in vibratory motion and static frictionotherwise troublesome in the mid-region of the pile is virtuallyeliminated.

I claim:

1. The method of driving a pile made of an elastic medium into theearth, that comprises: resting the lower end of the pile on the earth,and engendering in said pile a longitudinal standing wave having twodifferent resonant frequency components.

2. The method of driving a pile made of an elastic medium into theearth, that comprises: resting the lower end of the pile on the earth,and engendering in said pile a longitudinal standing wave havingfundamental and second harmonic frequency components.

3. The method of driving a pile made of an elastic medium into theearth, that comprises: resting the lower end of the pile on the earth,and engendering in said pile a longitudinal standing wave havingfundamental and harmonic frequency components.

4. The method of driving a pile made of an elastic medium into theearth, that comprises: resting the lower end of the pile on the earth,engendering in said pile a longitudinal standing wave having twodifferent resonant frequency components, and exerting a downward biasingforce on said pile.

5. The method of driving a pile made of an elastic medium into theearth, that comprises: engaging the pile with the earth, exerting adownward biasing force on the pile, engendering in the pile a resonantlongitudinal standing wave, and simultaneously therewith engendering inthe pile a higher frequency resonant longitudinal standing wave.

6. The method of driving a pile made of an elastic mevdium into theearth, that comprises: engaging the pile with tudinal resonant standingwave having a higher frequency Y to provide a closer spacing betweenVelocity nodal and vantinodal points than said irst mentioned'standingwave.

2,670,943 3/54 Vogel i 175-56 X y2367,984v v 1/59 Desvauxetal 175552,975,846 3/61 Bodine 175-56 X 3,054,463 9/62 Y Bodine 175-19 VFOREIGNPATENTS Y726,660 {1o/42 Germany.

CHARLES E. OCONNELL, Primary Examiner.

1. THE METHOD OF DRIVING A PILE MADE OF AN ELASTIC MEDIUM INTO THEEARTH, THAT COMPRISES: RESTING THE LOWER END OF THE PILE ON THE EARTH,AND ENGENDERING IN SAID PILE A LONGITUDINAL STANDING WAVE HAVING TWODIFFERENT RESONANT FREQUENCY COMPONENTS.